The present invention relates to the treatment of pigments and fillers using alkylsilanes and alkylsilane copolymers. The alkylsilane copolymers are prepared by the hydrolysis and condensation of monomeric or oligomeric silanes. The alkylsilanes and alkylsilane copolymers are particularly useful in the surface treatment of minerals for improving the dispersibility and processibility of the minerals in polymeric compositions. In particular, the alkylsilane copolymers of the present invention find particular utility in the surface treatment of titanium dioxide which is subsequently compounded with polyolefins, especially low density polyethylene. The alkylsilanes find particular utility in the silanization of clays, nanoclays, aluminum trihydroxides and magnesium hydroxides.
Organo compounds have been extensively employed in the surface treatment of inorganic particulate materials such as inorganic oxide materials such as films, particulate fillers and pigments, and fibers (such as glass fibers, aluminum fibers and steel fibers) which act to reinforce resins or plastic materials into which it is incorporated.
The typical organosilicon treatment involves coating such surfaces with a hydrolyzate (and/or condensate of the hydrolyzate) of an organofunctional hydrolyzable silane.
In particular, organosilicon compounds have been used to modify pigments such as titanium dioxide in order to alter the dispersion characteristics of the pigment in a given matrix. Matrix materials commonly used include thermoplastic polymers such as low density polyethylene. Such treatment of titanium dioxide is well known in the art. For instance, U.S. Pat. No. 4,061,503 discloses the treatment of particulate titanium dioxide with a polyether substituted silicon compound for improving the dispersibility of titanium dioxide in pigmented and/or filled paints and plastics, and reinforced plastic composite compositions. The silane compound is described and claimed as having at least two hydrolyzable groups bonded to the silicon and an organic group which contains a polyalkylene oxide group, the silane being present on the surfaces of the titanium dioxide particles in an amount sufficient to improve the dispersibility of the particles in a resin or plastic medium.
U.S. Pat. No. 4,151,154 discloses a modified hydrophobic colored or magnetic pigment or filler comprising a hydrophobic pigment or filler containing from 0.05 to 10% by weight, based on the weight of the pigment or filler, or an organopolysiloxane.
Further, U.S. Pat. No. 4,810,305 discloses a modified hydrophobic pigment or filler containing 0.05 to 10 weight % of an organopolysiloxane with improved dispersibility in synthetic resins, and U.S. Pat. No. 5,607,994 and U.S. Pat. No. 5,631,310 disclose the use of alkylsilane for the treatment of TiO2 to improve processibility in compounding with plastics and improve performance properties such as lacing resistance in a polymer matrix.
U.S. Pat. No. 4,950,779 describes a nonaqueous method of making silicone oligomers by using stoichiometric amounts of formic acid to effect the condensation of polyalkyoxysilanes or polyaminosilanes.
U.S. Pat. No. 5,932,757describes a mixture of oligomers of condensed alkylalkoxysilanes suitable for application in particular, to mineral surfaces, which substantially prevents wetting of the mineral surfaces by a hydrophilic liquid.
The present inventors have found that the hydrolysis and condensation of different silanes, as opposed to the self condensation of a single silane or silane oligomer, i.e. monomers, can produce alkylsilane copolymers and terpolymers which have a broader range of performance capabilities than a homopolymer. The alkylsilane copolymers and terpolymers of the present invention may be utilized for the surface treatment of fillers, pigments and so forth to improve the dispersibility of such compounds in a thermoplastic resins or polymers, including olefinic polymers such as low density polyethylene, even at extremely high loading levels. The treated filler or pigments of the present invention exhibit excellent compounding processibility, dispersion, and optical properties including whiteness and yellowness index, when blended with olefinic polymers in contrast to untreated fillers and pigments, or fillers and pigments treated with single silanes or silane oligomers or homopolymers. In particular, the present invention has found utility in the treatment of titanium dioxide pigment for improved dispersibility in low density polyethylene.
The present invention relates to the surface treatment of pigments and fillers with alkylsilanes and alkylsilane copolymers.
The alkylsilane copolymers of the present invention are prepared by hydrolysis and condensation of monomeric and/or oligomeric silanes. The alkylsilane copolymers have a plurality of hydrolyzable groups and comprise, in their backbone structures, at least two different monomers.
More specifically, the alkylsilane copolymer of the present invention has the following general structure:
R[SiR1R2O]mxe2x80x94[SiR3R4O]nR5
where
R, R1, R4 and R5 are hydrolyzable groups such as alkoxy, halogen, acetoxy, hydroxy, and so forth, or mixture thereof;
R2 is a nonhydrolyzable C1-C20, aliphatic, cycloaliphatic or aromatic hydrocarbon group directly or indirectly bonded to the silicon atom;
R3 is selected from nonhydrolyzable and hydrolyzable groups different from R2;
and m and n are each independently 1 to 20.
The alkylsilanes may also be terpolymers of the following general formula:
R[SiR1R2O]mxe2x80x94[SiR3R4O]nxe2x80x94[SiR6R7O]pR5
where R, R1, R2, R3, R4 and R5 are as described above;
R6 may be a nonhydrolyzable group as defined for R3 but different from R2 and R3;
R7 is a hydrolyzable group such as alkoxy, halogen, acetoxy, hydroxy, and so forth, or mixture thereof; and
m, n and p are each independently 1 to 20.
The alkylsilanes are alkyltrialkoxysilanes.
The alkylsilane copolymers and alkylsilanes of the present invention can be used to surface treat or silanize mineral type compounds such as pigments or fillers. In particular, the alkylsilanes are useful for the silanization of clays, nanoclays, aluminum trihydroxides and magnesium hydroxides.
This surface treatment or silanization improves the dispersibility and processibility of the pigments or minerals when compounded with polymeric materials. The materials require lower torque and pressure when melt compounded with polymeric materials in extruders.
The surface treated or silanized pigments or fillers of the present invention, in addition to the improvements noted above, also exhibit excellent optical properties including whiteness and yellowness index, hue, chroma and gloss.
The compounds that can be treated or silanized using the alkylsilanes and alkylsilane copolymers and terpolymers of the present invention include pigments and fillers, inorganic particulate materials such as inorganic oxide materials such as films, and fibers (such as glass fibers, aluminum fibers and steel fibers) which act to reinforce resins or plastic materials into which it is incorporated. In particular, alkylsilanes and alkysilane copolymers and terpolymers can be used to treat white pigments and fillers.
Some specific materials for surface treatment or silanization include calcined clay, nanoclay, aluminum trihydroxide, magnesium hydroxide, and so forth. In particular, the alkylsilane copolymers of the present invention can be used to treat titanium dioxide which is often used as a pigment.
The TiO2 pigments useful in the present invention generally are in the rutile or anatase crystalline form. They are commonly prepared by either a chloride process or a sulfate process. The optimum average particle size can range from about 0.005 to about 1 micron. The TiO2 pigments may also contain ingredients added thereto to further improve dispersibility characteristics or other properties such as durability. For instance, the pigment may contain additives and/or inorganic oxides, such as aluminum, silicon or tin as well as triethanolamine, trimethylopropane, phosphates, etc.
xe2x80x9cTreatedxe2x80x9d pigments or fillers are defined herein to refer those pigments or fillers surface treated with at least one alkylsilane copolymer, or a mixture of at least one alkylsilane copolymer and at least one triorganosilyl terminated nonhydrolyzable polydiorganosiloxane (collectively referred to herein as organosilicon compounds).
xe2x80x9cSilanizedxe2x80x9d pigments or fillers are defined herein to refer to those pigments or fillers surface treated with at least one single alkylsilane or alkylsilane monomer.
According to the present invention, silane monomers of different chemical structures can be hydrolyzed or condensed to form copolymers, terpolymers, and so forth. The alkylsilanes of the present invention must be formed with at least two different monomers, but no limit is placed on how many different monomers may be utilized. Hereinafter, the present specification will refer to the structures generally as copolymers, although reference is also made to terpolymers, without intent to limit the number of different monomers utilized, to three. For instance, four monomers or more, could be conceivably used to form the polymers of the present invention.
The use of different monomers in the alkylsilane copolymer backbone can result in a polymer having different functional groups in the comonomers. The dual functionality of the copolymer can provide stronger coupling to the fillers and better compatibility to the base resin. For instance, if one monomer is unsaturated such as a vinyl, a crosslinking function can be provided in addition to the coupling and compatibility functions. Terpolymers can be designed using precondensation to provide three different functions including coupling, crosslinking and compatibility with the polymer resin depending on the type of silane or silicon compound chosen, and the pendant functional groups that silane or silicon compounds have.
The alkylsilane copolymers are commercially available, or can be prepared by processes known in the art such as those described in xe2x80x9cOrganosilicon Compoundsxe2x80x9d, S. Pawlenko, et al., New York (1980), the teachings of which are incorporated herein by reference. Copolymers may be prepared from silanes having at least 2 hydrolyzable groups through hydrolysis and condensation reactions. Silanes with a single hydrolyzable group may be utilized to endcap the copolymers. Hydrolysis of silanes is described in greater detail in xe2x80x9cOrganofunctional Silanesxe2x80x9d by Union Carbide (1991), the teachings of which are incorporated herein by reference.
The condensation reaction can be accelerated by using formic acid and a catalyst. The condensation reaction leads to a large portion of the alkoxy groups being pre-condensed prior to treatment of the pigments or fillers, e.g. TiO2, which subsequently leads to a faster reaction rate during the treatment. Furthermore, the precondensed copolymers produce less VOC""s during the treatment of minerals.
The alkylsilane copolymers and terpolymers of the present invention may be formed using a variety of combinations including, for instance, an alkylsilane with 2 or 3 hydrolyzable groups such as alkoxy, acetoxy, hydroxy, or halide (in particular chloride), co-condensed with at least one second silane having at least 2 hydrolyzable groups such as methacryloxypropylsilane or vinyltrialkoxysilane, any silicon compound having at least 2 hydrolyzable groups such as tetraethylsilicate or tetramethylsilicate, or a linear or cyclic organosilicon compound such as tetracyclodimethylsiloxane (D4).
More specifically, examples of suitable silane monomers useful in forming the copolymers and terpolymers of the present invention include, but are not limited to, alkyltrialkoxysilanes such as Silquest(copyright) A-162 methyltriethoxysilane supplied by Crompton Corp. in Middlebury, Conn.; Silquest(copyright) A-1630 methyltrimethoxysilane; Silquest(copyright) A-137 octyltriethoxysilane; and Silquest(copyright) Y-11869 octadecyltriethoxysilane all supplied by Crompton, Corp. In one embodiment of the present invention, Silquest(copyright) A-137 octyltriethoxysilane is utilized.
Other alkylsilane monomers useful herein include, but are not limited to, butyltriethoxysilane, dodecyltriethoxysilane, octyltrimethoxysilane, octadecyltrimethoxysilane, butyltrimethoxysilane, dodecyltrimethoxysilane, and mixtures thereof.
The alkylsilane copolymers of the present thus have a plurality of hydrolyzable groups, and at least two different monomers in their backbone structure. By a xe2x80x9cpluralityxe2x80x9d it is meant 2 or more, preferably 3 or more, and more preferably 4 or more hydrolyzable groups.
The silane copolymers of the present invention may be characterized by the following general formula:
xe2x80x83R[SiR1R2O]mxe2x80x94[SiR3R4O]nR5
where
R and R1 are hydrolyzable groups such as alkoxy, halogen, acetoxy, hydroxy, and so forth, or mixture thereof;
R2 is a nonhydrolyzable C1-C20, aliphatic, cycloaliphatic or aromatic alkyl group directly or indirectly bonded to the silicon atom;
R3is selected from nonhydrolyzable and hydrolyzable groups different from R2, for instance R3 may be a nonhydrolyzable group such as alkyl, which may be optionally substituted with epoxy, amino, mercapto, ureido (H2NC(xe2x95x90O)NHxe2x80x94), or interrupted with one or more sulfur or oxygen atoms, alkenyl, (e.g. vinyl, allyl, methallyl, hexenyl, etc), (alk)acryloxyalkyl (e.g. acryloxypropyl or methacryloxypropyl), and aryl, or R3 may be a hydrolyzable group such as alkoxy, halogen, acyloxy (e.g. acetoxy, (alk)acryloxy, etc.), hydroxy mercapto, amino or mixtures thereof;
R4 and R5 are hydrolyzable groups including alkoxy, halogen, acetoxy, hydroxy, and so forth, or mixture thereof;
and m and n are each independently 1 to 20.
In some particular embodiments of the present invention, the silane copolymer utilized is octyltriethoxysilane/tetraethoxysilicate.
The silane terpolymers of the present invention have the following general structure:
R[SiR1R2O]mxe2x80x94[SiR3R4O]nxe2x80x94[SiR6R7O]pR5
where
R and R1 are hydrolyzable groups such as alkoxy, halogen, acetoxy, hydroxy, and so forth, or mixture thereof;
R2 is a nonhydrolyzable C1-C20, aliphatic, cycloaliphatic or aromatic alkyl group directly or indirectly bonded to the silicon atom;
R3 is selected from nonhydrolyzable and hydrolyzable groups different from R2;
R4 and R5 are hydrolyzable groups such as alkoxy, halogen, acetoxy, hydroxy or mixtures thereof;
R6 may be a nonhydrolyzable group such as alkyl, vinyl, methacryloxy, or any unsaturated double bond rather than vinyl, or may be a hydrolyzable group such as alkoxy, halogen, acetoxy, hydroxy, and so forth, or mixture thereof;
R7 is a hydrolyzable group such as alkoxy, halogen, acetoxy, hydroxy, and so forth, or mixture thereof; and m, n and p are each independently 1 to 20.
The copolymers thus formed can then be used to treat fillers or pigments, specifically titanium dioxide (TiO2), to improve the dispersibility, compounding processibility, and in the case of pigments, to improve the whiteness, when compounded with polymeric resins, and in particular when compounded with olefinic polymers. Using the precondensed silane copolymers of the present invention provides an advantage over single alkylalkoxysilanes in that lower VOC""s, particularly lower alcohol emission including methanol and ethanol emission, are produced during treatment of the pigment or filler in contrast to using a single silane, i.e. oligomeric or monomeric, alkylalkoxysilanes, for instance. The precondensation of the alkoxy groups during the copolymerization results in less alcohol formation during the treatment of minerals with the silane copolymers, the latter also occurring through hydrolysis and condensation.
The copolymers are useful from about 0.1 wt-% to about 5 wt-% based on the weight of the treated pigment or filler, and preferably from about 0.5 wt-% to about 3 wt-%.
Optionally, the copolymers of the present invention may be used in combination with a polysiloxane. Suitable polysiloxanes have the following general formula:
(RnSiO(4-n)/2)m
wherein
R is an organic or inorganic group;
n is 0 to 3; and
m is equal or greater than 2.
In addition to the treatment of minerals with copolymers and terpolymers, the present inventors have found that single alkylsilanes may be utilized to treat certain minerals including nanoclays, clays, aluminum trihydroxides, and magnesium hydroxides. The alkylsilanes useful for such treatment include the alkyltrialkoxysilanes noted above. In particular, the alkyltrimethoxysilanes and alkytriethoxysilanes including but not limited to methyltrimethoxysilanes, octyltrimethoxysilanes, butyltrimethoxysilanes, dodecyltrimethoxysilanes, octadecyltrimethoxysilanes, methyltriethoxysilanes, octyltriethoxysilanes, butyltriethoxysilanes, dodecyltriethoxysilanes, octadecyltriethoxysilanes, and so forth.
The alkylsilanes and alkylsilane copolymers may be used in combination with nonhydrolyzable polysiloxanes. Examples of useful polysiloxanes include the group of triorganosilyl terminated polydiorganosiloxanes including Silwet(copyright) L-45 polydimethylsiloxane (PDMS) available from Crompton Corp. in Middlebury, Conn., vinyl phenylmethyl terminated dimethyl siloxanes, divinylmethyl terminated PDMS and like, PDMS with polyether pendant groups (Silwet(copyright) PA-1), and so forth. In some particular embodiments of the present invention, PDMS sold under the trade name of Silwet(copyright) L-45 PDMS, is utilized.
The polysiloxanes are also commercially available, or can be prepared by processes known in the art such as those described in xe2x80x9cOrganosilicon Compoundsxe2x80x9d, S. Pawlenko, et al., New York (1980), the teachings of which are incorporated herein by reference.
The combination of copolymer and/or nonhydrolyzable siloxane is useful from about 0.1 to about 5.0% by weight, preferably from about 0.5 to about 4.0% by weight, and most preferably from about 0.5 to about 3.0% by weight based on the treated pigment or filler. A preferred blend includes from about 0.5 to 2.0% by weight of the silane copolymer and from about 0.5 to about 2.0% by weight of the polysiloxane. The ratio of silane copolymer to nonhydrolyzable polysiloxane may be from about 1:2 to about 2:1, and is preferably about 1:1.
The method of addition is not especially critical and the pigment or filler may be treated with the alkylsilane copolymer in a number of ways. For example, the silane addition can be made neat or prehydrolyzed to a dry pigmentary base, from a slurry, a filtration step, during drying or at a size operation such as fluid energy mill, e.g., micronizer, or media mill as described in greater detail in U.S. Pat. No. 5,501,732, the teaching of which are incorporated herein by reference, or post blending after micronizing.
U.S. Pat. No. 3,834,924 describes organosilane and pigment dispersions mixed or blended directly in a suitable solids mixing apparatus. An example of post blending is described in greater detail in U.S. Pat. No. 3,915,735 and U.S. Pat. No. 4,141,751. The nonhydrolyzable polydiorganosiloxane addition can be made in conjunction with the silane or post added to the treated pigment. The silane addition and polysiloxane addition are described in greater detail below. If water, either liquid or vapor (steam), is present as a component of the process stream, hydrolysis of the hydrolyzable groups of the silane will occur and the silane coating will bond to the pigment, for instance TiO2, base. Prehydrolyzing the alkylsilane copolymer is a preferred step in treating the pigment with the silane copolymer.
The alkylsilane or alkylsilane copolymer, optionally in combination with a nonhydrolyzable polysiloxane, may be coated on the surface of the pigment or filler in an amount of about 0.1% to about 5.0% by weight of the treated titanium dioxide, and preferably from about 0.5% to about 3.0% by weight according to the present invention.
The treated pigments or fillers of the present invention may be used in combination with any polymeric material with which such compounds are typically used. The alkylsilane copolymer acts, in a sense, as a dispersion promoter, by increasing the compatibility and dispersibility of the inorganic oxide or other particulate material within the plastic or resin system in which it is supplied.
The polymers useful herein are known to those of skill in the art. Typically, the general classes of polymers suitable for use herein are thermoplastic, or are thermosetting polymeric resinous materials, and include but are not limited to, polymers of ethylenically unsaturated monomers including olefins such as polyethylene, polypropylene, polybutylene, and copolymers of ethylene with higher olefins such as alpha olefins containing 4 to 10 carbon atoms or vinyl acetate, etc.; vinyls such as polyvinyl chloride; polyvinyl esters such as polyvinyl acetate; polystyrene; acrylic homopolymers and copolymers; phenolics; alkyds; amino resins; epoxy resins; polyamides; polyurethanes; phenoxy resins; polysulfones; polycarbonates; polyesters and chlorinated polyesters; polyethers; acetal resins; polyimides; and polyoxyethylenes. The polymers according to the present invention also include various rubbers and/or elastomers either natural or synthetic polymers based on copolymerization, grafting, or physical blending of various diene monomers with the above mentioned polymers, all as generally known in the art. Thus generally, the present invention is useful for any such white-pigmented plastic or elastomeric compositions (collectively referred to herein as white-pigmented polymers). For example, but not by way of limitation, the invention is felt to be particularly useful for polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyamides and polyesters.
Polymeric materials useful to the present invention are discussed in U.S. Pat. No. 4,061,503 and U.S. Pat. No. 4,151,154, both incorporated by reference herein in their entirety.
In some particular embodiments of the present invention, the polymers chosen for use include polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyamides, polyesters and copolymers and terpolymers thereof.
The term xe2x80x9chigh loadedxe2x80x9d TiO2 may vary widely, depending on the type of polymer used and may be anywhere from about 40 wt-% TiO2, to greater than 85 wt-% TiO2. For instance, in a polyolefin matrix, a high loaded TiO2 would be 50 wt-% or more of the TiO2 pigment, based on the total weight of polyolefin matrix. Such a determination is within the knowledge of those of skill in the art.
A wide variety of conventional additives may be optionally added to the polymeric compositions of the present invention as is necessary, desirable or conventional for the intended end use. Such additives include but are not limited to antioxidants, ultraviolet (UV) stabilizers, lubricants, thermal processing additives, and so forth. Such additives are known to those of skill in the art.
Pigment or filler coated with organosilicon compounds can be incorporated into a melt-fabricable polymer to form the polymeric compositions of the present invention by any melt compounding technique known to those of skill in the art. Generally, pigment and polymeric resin are added together, and are subsequently mixed in a blending apparatus that applies shear to the polymer melt. The polymeric resin is typically commercially available in a variety of forms including but not limited to powder, granules, pellets, cubes, and so forth.
In a typical mixing operation, pigment and polymer are first combined and are dry blended while the polymer is still in a solid, premelted state. This can be accomplished with simple processes such as by shaking in a bag or by tumbling in a closed container. More sophisticated methods include blending apparatuses having agitators or paddles. The pigment and the polymeric resin can be co-fed into mixers having an internal screw, i.e. an extruder device, which mixes the pigment and polymer prior to the polymer achieving a molten state.
Melt blending the components may be accomplished using any conventional equipment known to those of skill in the art including single-screw extruders, twin-screw extruders including the broad range of counter-rotating twin screw extruders and co-rotating twin screw extruders, kneaders, high shear mixers, blender type mixers, and so forth. Twin-screw extruders are commonly used. The melt blending can be accomplished during formation of an article such as during a melt extrusion process. Melt extrusion can also be combined with blow molding, for instance.
Exemplary mixers include twin screw extruders and Banbury mixers. Co-rotating twin screw extruders are manufactured by Werner and Pfleiderer in Ramsey, N.J. Counter-rotating twin screw extruders are manufactured by Leistritz Extruder Corp. in Somerville, N.J. Farrel Corp. in Ansonia, Conn. manufactures Banbury mixers.
There are numerous ways of preparing the polymeric compositions of the present invention. A concentrate may first be prepared having a high concentration of pigment or filler, and then subsequently combine the concentrate with polymeric resin. The highly loaded polymer concentrates are made as described above with the desirable weight-% of pigment for the intended end use. For example, in polyolefin concentrates, about 50-85% by weight concentrate may be used to opacity the composition. The pigment concentrate is xe2x80x9clet downxe2x80x9d into the polymer. As used herein, xe2x80x9clet downxe2x80x9d refers to a ratio or percentage of polymer mixed with concentrate. Let down may be accomplished in a number of ways and is described in great detail in xe2x80x9cFilm Extrusion Manualxe2x80x9d (1992), the teachings of which are incorporated herein by reference. For example, in optical property evaluation, a 50 wt-% to 87 wt-% concentrate may be let down to about 0.2 to 30 wt-% by dry mixing polyolefin, extruding at a specific temperature, and casting it into a film. The pigment performance is then evaluated in an end use application.
The highly loaded treated pigment or filler exhibits outstanding processibility in polyolefinic matrices, and excellent lacing resistance. The torque and pressure can be utilized to determine the relative ease with which the compositions are processed through a mixer, e.g. an extruder, for instance. The lower the torque and pressure required to mix and move the composition through the equipment, the easier the processing is. Furthermore, typically, the higher the loading of pigment or filler, for example TiO2, in a polymer concentrate, the slower the processing rates.
The compositions of the present invention require lower torque and pressure for processing, particularly through an extruder, than do those polymeric compositions compounded with untreated pigment or filler, and faster processing rates can also be obtained.
Lacing refers to the development of imperfections in a polyolefin matrix. Lacing occurs as a result of volatiles released from the pigment during high temperature polyolefin fabrication processes. Lacing may also be attributable to, for instance, TiO2 concentrates picking up moisture. More specifically, lacing occurs as a function of pigment volatility at specific wt-% of pigment loadings and at specific processing temperatures. For polyethylene films pigmented with titanium dioxide, 20% wt-% TiO2 in the film processed at temperature of 620xc2x0 F. or greater will readily exhibit lacibility of the film. Typically, materials are rated on a scale of 1 to 10. The materials will be rated a 10 if they do not exhibit any lacing, and below 10 if they begin to lace. Lacing resistance is known to one of skill in the art and is also discussed in U.S. Pat. No. 5,607,994 and U.S. Pat. No. 5,631,310, both incorporated by reference herein in their entirety.
Other advantages include increased bulk density, lower viscosity, excellent dispersion, excellent moisture resistance, and excellent optical properties such as high whiteness and gloss.
The polymeric materials containing the treated particles of the present invention are useful in a variety of applications including various articles. The polymeric compositions of the present invention may be employed, for example, for molding (including extrusion, injection, calendering, casting, compression, lamination, and/or transfer molding), coating (including lacquers, film bonding coatings and painting), inks, dyes, tints, impregnations, adhesives, caulks, sealants, rubber goods, and cellular products. Thus the choice and use of the polymeric compositions with the treated particles of this invention is essentially limitless.
One of ordinary skill in the art would understand that there are a vast number of modifications which could be made without changing the scope of the invention, those modifications and embodiments thereof are contemplated to be within the scope of the present invention.
Optionally, other additives may be used in the compositions of the present invention including, but not limited to antioxidants, ultraviolet (UV) stabilizers, lubricants, thermal processing additives, and so forth. Such additives, as well as others not mentioned here, are known to those of skill in the art.
Pigments or fillers coated with organosilicon compounds can be incorporated into a melt-fabricable polymer to form the polymer composition of this invention by any melt compounding technique known in the art. Generally, pigment and/or filler, and polymer resin are brought together and then mixed in a blending operation that applies shear to the polymer melt. The polymer resin is usually available in the form of powder, granules, pellets, or cubes. Usually, pigment and/or filler and resin are first combined while the resin is in the solid state (not melted) and dry-blended in some way. This can be done in simple ways, such as by shaking in a bag or tumbling in a closed container, or in more sophisticated ways such as by using blends having agitators or paddles. Pigment and/or filler and polymer resin can be brought together by co-feeding the materials to internal mixers and allow a screw to mix them together before the resin reaches the molten state. The melt blending of pigment and/or filler and polymer resin can be done using known equipment, such as single-screw extruders, twin-screw extruders, internal mixers and the like. Twin-screw extruders are commonly used. The melt blending can be done as part of the process of forming a finished article of the composition, as by melt extrusion.
There are many ways for preparing polymer compositions of this invention. One may, for example, first prepare a concentrate having high pigment and/or filler concentration, and then combine or further compound the concentrate with polymer resin containing no pigment or filler.
The treated pigments or fillers may be incorporated into a polymeric resin system with or without the addition of a silicon fluid such as a polydimethylsiloxane.
The treated pigments or fillers of the present invention are useful when compounded with polymeric materials in the range of about 0.01% to about 90% by weight of the polymer/treated pigment or filler composition. The treated pigments or fillers of the present invention can be utilized with polymers, in particular low density polyethylene, at very high loading levels of as much as 90 wt-% pigment or filler based on the weight of the composition. Highly loaded polymer concentrates can be made as described above with the desirable weight-% for the intended end use. For example, in polyolefin concentrates, about 40-85% by weight concentrate may be used to opacify. The concentrate is xe2x80x9clet downxe2x80x9d into the polyolefin. Used herein, xe2x80x9clet downxe2x80x9d refers to a ratio or percent of resin mixed with concentrate. Let down may be accomplished in a number of ways and is described in great detail in xe2x80x9cFilm Extrusion Manualxe2x80x9d (1992), the teachings of which are incorporated herein by reference. For example, in optical property evaluation, a 50 wt-% to 87 wt-% concentrate may be let down to about 0.2 to about 30 wt-% by dry mixing polyolefin, extruding at a specific temperature and casting it into a film. Pigment performance, for instance, is then evaluated in an end use application.
The treated or silanized pigments and/or fillers of the present invention exhibit outstanding processibility, faster output, and better dispersion when incorporated into a polymeric system, i.e. a polyolefin matrix, even at very high loadings, versus using an untreated pigments. Additional advantages observed over systems using an untreated pigment include increased bulk density, lower viscosity, high moisture resistance, and excellent optical properties such as a higher whiteness and gloss and a lower yellowness index. The mechanical properties exhibited by the polymeric system was also improved.